The Optimization Of Fermentation Medium Of Propionibacterium Shermanii And Characteristics Of Its Antimicrobial Metabolites

The antimicrobial metabolites from Propionibacterium is a kind of potential andnatural food preservatives. At present，the medium for studying and producingPropionibacterium antimicrobial metabolites is expensive, which limits the industrialproduction and application of antimicrobial metabolites. In this thesis, thefermentation medium of Propionibacterium shermanii which can produceantimicrobial metabolites was optimized, the properties of antibacterial metaboliteswere analyzed, and the antibacterial metabolites were preliminary purified.The fermentation medium was optimized to reduce the medium cost and promotethe antimicrobial metabolites production of Propionibacterium shermanii by simplefactor experiment and response surface methodology. The results showed that theyeast extract and tryptone of original medium could be replaced by the corn steepliquor power and soy peptone. According to Box-Behnken design and responsesurface methodology, the optimal medium were as follows:8.2g/L glucose,5.1g/Lsoy peptone, and12.7g/L corn steep liquor. After medium optimization, the theoryvalue of antimicrobial activity was29.5AU/mL and the actual activity was29.4AU/mL. The antimicrobial activity was improved by57.8%. and the medium cost wasreduced.Two kinds of whey powder, three kinds of skimmed milk powder andconcentrated whey protein were chosen as main ingredients of the fermentationmedium to develop a fermentation medium containing dairy raw as main components.The results showed that the bacteriostatic activity of metabolites was high with thevalue of26.3AU/mL when whey powder was used as the main ingredients of themedium. The highest bacteriostatic activity was got with the value of29.4AU/mLwhen80g/L whey powder A was added.The properties of antimicrobial metabolites of Propionibacterium shermanii werepreliminary researched. The metabolites of Propionibacterium shermanii was thermal stability and still kept good antibacterial activity after treatment at121℃for20min. The antibacterial activity of Propionibacterium shermanii metabolites wereeffected by pH. Its activity was highest at the pH5.5and greatly reduced or evendisappeared when in the neutral or alkaline pH. Part of activity lost and the inhibitionzone become small significantly when the Propionibacteria metabolites were treatedwith pepsin and trypsin,Metabolites of Propionibacterium shermanii have bacteriostatic effect onPseudomonas putida, Alicyclobacillus acidoterrestris, Kluyveromyces marxianus.Pseudomonas putida showed the strongest,sensitivity to Propionibacteriumshermanii, then followed Alicyclobacillus acidoterrestris and Kluyveromycesmarxianus.Metabolites of Propionibacterium shermanii were separated and purified and itsstructural properties were analyzed preliminary. Preliminary purification products ofPropionibacterium shermanii were obtained by centrifugation, concentrated,microfiltration, ultrafiltration, desalting chromatography and column chromatographypurification successively. The antibacterial activity, relative molecular mass, structuretype and functional group of the products were analyzed by antibacterial activity test,TLC chromatography, MALDI-TOF mass spectrometry and Fourier transforminfrared spectroscopy. At least one peptide substances with strong antibacterialactivity were contained in inhibitory metabolites of Propionibacterium shermanii. Itsmolecular mass was701.5. It was a high polar molecule, and an unsaturated doublebond such as carbonyl groups were existed in its molecular structure. Theantibacterial activity of Propionibacterium shermanii metabolites after separation andpurification was increased more than three times compared with original products.